The magnetic link between star and planet

Astronomers say that they have for the first time directly measured the magnetic field of a star known to host a giant planet.

Although the magnetic field of the star, called Tau Boötes, is only a few times as strong as that of the sun, it probably wields enormous influence on the planet, say the researchers. That's because the orb whips around Tau Boötes at just one-twentieth the distance that Earth circles the sun.

To measure the field, Claude Catala of the Observatory of Paris and his colleagues examined the polarization of light from the star using a device on the Canada-France-Hawaii Telescope on Hawaii's Mauna Kea. Light waves are composed of electric and magnetic fields that oscillate in specific directions. The extent to which light coming from the star is polarized indicates the strength of a magnetic field along a particular direction.

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